Cleaving process to fabricate multilayered substrates using low implantation doses

ABSTRACT

A method of forming substrates, e.g., silicon on insulator, silicon on silicon. The method includes providing a donor substrate, e.g., silicon wafer. The method also includes forming a cleave layer on the donor substrate that contains the cleave plane, the plane of eventual separation. In a specific embodiment, the cleave layer comprising silicon germanium. The method also includes forming a device layer (e.g., epitaxial silicon) on the cleave layer. The method also includes introducing particles into the cleave layer to add stress in the cleave layer. The particles within the cleave layer are then redistributed to form a high concentration region of the particles in the vicinity of the cleave plane, where the redistribution of the particles is carried out in a manner substantially free from microbubble or microcavity formation of the particles in the cleave plane. That is, the particles are generally at a low dose, which is defined herein as a lack of microbubble or microcavity formation in the cleave plane. The method also includes providing selected energy to the donor substrate to cleave the device layer from the cleave layer at the cleave plane, whereupon the selected energy is applied to create a controlled cleaving action to remove the device layer from a portion of the cleave layer in a controlled manner.

This is a continuation of Ser. No. 09/370,959 filed Aug. 10, 1999, abnd.

BACKGROUND OF THE INVENTION

The present invention relates to the manufacture of objects. Moreparticularly, the invention provides a technique including a method anddevice for cleaving a substrate in the fabrication of a multi-layeredsubstrate for semiconductor integrated circuits, for example. But itwill be recognized that the invention has a wider range ofapplicability; it can also be applied to other substrates formulti-layered integrated circuit devices, three-dimensional packaging ofintegrated semiconductor devices, photonic devices, piezoelectronicdevices, microelectromechanical systems (“MEMS”), sensors, actuators,solar cells, flat panel displays (e.g., LCD, AMLCD), biological andbiomedical devices, and the like.

Many ways of fabricating substrates for the manufacture of integratedcircuits have been proposed. In the early days, conventional integratedcircuits were fabricated on “bulk” silicon wafers. These bulk siliconwafers were generally single crystal and formed using a process calledCzochralski, which is known as CZ. The CZ process melts a batch ofsilicon metal in a crucible. A seed crystal is used as a startingmaterial to pull a silicon ingot from the melt in the crucible. Theingot is then cut and polished to form the bulk silicon wafers.

Although bulk silicon wafers are widely used today, many such wafershave been replaced by other types. These other types of wafers include,among others, epitaxial silicon wafers, silicon-on-insulator wafers, andthe like. High purity applications often require the use of epitaxialsilicon wafers. These applications often produce lower yields on CZwafers so such epitaxial silicon wafers are desirable. High purityapplications include the manufacture of high density memory devices,high voltage devices, and microprocessor devices.

Some applications also use silicon on insulator wafers. These wafersgenerally include a silicon material layer, where devices are to beformed, overlying an insulating layer, commonly made of silicon dioxide,which overlies a bulk substrate material. Silicon on insulator wafers,which are known as SOI wafers, are made using one of many techniques. Acommon technique for making such wafer is “separation by ionimplantation of oxygen,” also termed as SIMOX. These SIMOX wafers areoften made by implanting high doses of oxygen impurities into a siliconsubstrate, where the oxygen is later annealed to create an insulatinglayer underlying a surface of the silicon substrate. An active devicelayer is defined overlying such insulating layer. SIMOX wafers, however,have numerous limitations. For example, SIMOX wafers are often difficultto make in an efficient manner, since the high doses often require along implantation time. Implantation is generally an expensive operationin the manufacture of wafers. Additionally, implantation of oxygen oftencauses damage to the device layer. Such damage can influence theoperation and reliability of integrated circuit devices that arefabricated onto the device layer.

Accordingly, other ways of developing SOI wafers have been proposed. Onesuch way is a “blistering” method for film separation known as SmartCut™. Such blistering technique is described in detail in U.S. Pat. No.5,374,564, in the name of Bruel (“Bruel '564”). This thermal blisteringtechnique for manufacturing SOI wafers has many limitations. For highvolume production, the high doses of hydrogen often requires the use ofmany ion implanters, which are expensive and difficult to maintain.Additionally, thermal blistering often creates rough surface finishes,which can produce worthless scrap product. European Application No. EP0807970A1 (“Bruel '970”), which is also in the name of Bruel, suggestsan improved method to the Bruel '564 patent of forming SOI wafers. Bruel'970 suggests a method of mechanically separating a layer havingmicrocavities or microbubbles. Although the Bruel '970 suggests that thedoses are generally lower than a minimum causing surface blistering, thedoses of hydrogen should still be sufficiently high to allow microcavityand microbubble coalescence through a subsequent heat treatment process.Such thermal treatment process would often require a high temperature,which would lead to an exceedingly rough and imprecise fracturemorphology along the microcavity plane. Accordingly, the Bruel '970 alsorequires high temperatures, which are generally undesirable and lead toexcessive surface roughness characteristics.

Still another variation is described in U.S. Pat. No. 5,882,987, whichis assigned to International Business Machines Corporation, and in thename of Srikrishnan, Kris V (“Srikrishnan”). Srikrishnan suggests animprovement to the blistering technique taught by the Bruel '564 patent.Here, Srikrishnan suggests an etch-stop layer within a device layer tobe released. Additionally, Srikrishnan suggests implanting a large doseof hydrogen to allow separation using the aforementioned “blistering”process to separate the film at a location away from the etch-stoplayer, thereby resulting in a structure characterized by the devicelayer covered by the etch-stop layer and a top surface layer and thenselectively removing both layers. This process, which may beadvantageous by reducing or eliminating the need for achemical-mechanical polishing (CMP) step, still generally requires theuse of the blistering process, high doses of hydrogen or rare gas ionimplantation, and complicated chemical removals.

Yet another method for forming SOI wafers has been described in U.S.Pat. No. 5,854,123, which is assigned to Canon Kabushiki Kaisha, and inthe names of Sato, et al (“Sato”). The Sato patent suggests releasing anepitaxial layer, which has been formed on a porous silicon layer. Theporous silicon layer is generally made to release the epitaxial layer byproviding a high degree of etch selectivity between the epitaxialsilicon layer and the porous silicon layer. Unfortunately, thistechnique is often complicated and expensive. Moreover, epitaxial growthon a porous layer can compromise the quality of the epitaxial film bythe introduction of defects into it, which is very undesirable. Otherlimitations can also exist with such technique.

Accordingly, a pioneering technique made by a company called SiliconGenesis Corporation has been developed. Such technique relies upon acontrolled cleaving process, which is known as CCP, to manufacture SOIwafers and other structures. The CCP technique produces improved filmsusing a room temperature process to cleave films. The room temperatureprocess is generally free from microbubbles or microcavities, which maylead to blisters and the like caused by the conventional processdescribed in Bruel. Although overcoming many limitations in conventionaltechniques, CCP can still be improved.

From the above, it is seen that an improved method for manufacturingsubstrates is highly desirable.

SUMMARY OF THE INVENTION

According to the present invention, a technique including a method anddevice for manufacturing objects is provided. In an exemplaryembodiment, the present invention provides a method for fabricatingmultilayered substrates from a cleaving process. Such substrates use lowdoses of particles, which are used to create stress in a cleaving layer.The low doses of particles improve film quality and efficiency of thepresent method.

In a specific embodiment, the present invention provides a method offorming substrates, e.g., silicon on insulator, silicon on silicon. Themethod includes providing a donor substrate, e.g., silicon wafer. Themethod also includes forming a cleave layer on the donor substrate thatincludes a cleave plane, the plane along which the separation of thesubstrates occurs. In a specific embodiment, the cleave layer comprisingsilicon germanium. The method also includes forming a device layer(e.g., epitaxial silicon) on the cleave layer. The method also includesintroducing particles into the cleave layer to add stress in the cleavelayer. The particles are then redistributed where a portion of theparticles from the cleave layer forms a high concentration region of theparticles in a region within the cleave layer and adjacent to the devicelayer, where the redistribution of the particles is carried out in amanner substantially free from microbubble or microcavity formation ofthe particles. That is, the particles are generally at a low dose, whichis defined herein as a lack of microbubble or microcavity formation inthe cleave plane. The method also includes providing selected energy tothe donor substrate to cleave the device layer from the cleave layer atthe cleave plane, usually adjacent to the high concentration region ofparticles, whereupon the selected energy is applied to create acontrolled cleaving action to remove the device layer from the cleavelayer in a controlled manner.

In an alternative embodiment, the present invention provides a method offorming a multilayered substrate. The method includes providing a donorsubstrate. A cleave layer is formed on the donor substrate. The cleavelayer comprises silicon germanium. The method also includes forming adevice layer (e.g., epitaxial silicon) on the cleave layer. The methodalso introduces particles into the cleave layer to add stress in thecleave layer. A step of bonding a handle substrate on the cleave layer,and redistributing the particles where a portion of the particles fromthe cleave layer forms a higher concentration region of the particleswithin a region in the cleave layer. The redistribution of the particlesis carried out in a manner substantially free from microbubble ormicrocavity formation of the particles in the cleave plane. The methodalso includes providing selected energy to the donor substrate to cleavethe device layer from the cleave layer at the high concentration regionof particles, whereupon the selected energy is applied to create acontrolled cleaving action to remove the device layer from the cleavelayer along the cleave plane in a controlled manner to separate thehandle substrate that has the device layer from the donor substrate.

Still further, the present invention provides a composite substratecomprising a donor substrate. The substrate has an overlying cleavelayer, and has an overlying device layer, wherein the cleave layercomprises a maximum dosage of particles close to an interface betweenthe device layer and the cleave layer.

In an alternative embodiment, the present invention provides a method offorming substrates, e.g., silicon on insulator, silicon on silicon. Themethod includes providing a donor substrate, e.g., silicon wafer,epitaxial wafer, glass. The method includes forming a cleave layer(e.g., silicon germanium) comprising a cleave plane on the donorsubstrate. The method also includes forming a device layer (e.g.,epitaxial silicon) on the cleave layer. The method then introducesparticles into the cleave layer to add stress to the cleave plane, wherethe particles arc selected from those species that are derived free fromhydrogen gas, helium gas, or any other species that forms microbubblesor microcavities. As merely an example, such particles can be derivedfrom oxygen, silicon, germanium, nitrogen, and other species. The methodalso includes separating the device layer from the donor substrate atthe cleave plane of the donor substrate. Preferably, a controlledcleaving process is used.

Numerous benefits are achieved over pre-existing techniques using thepresent invention. In particular, the present invention uses controlledenergy and selected conditions to preferentially cleave a thin film ofmaterial from a donor substrate which includes multi-material sandwichedfilms. This cleaving process selectively removes the thin film ofmaterial from the substrate while preventing a possibility of damage tothe film or a remaining portion of the substrate. In other aspects, theprocess also provides a multilayered substrate structure, which can bereused without substantial damage. Accordingly, the remaining substrateportion can be re-used repeatedly for other applications. Still further,the method provides smoother films (e.g., less than 30 or 20 or 10 or 5or 3 or 2 Angstroms RMS) upon cleaving. Depending upon the application,one or more of these advantages may exist.

The present invention achieves these benefits and others in the contextof known process technology. However, a further understanding of thenature and advantages of the present invention may be realized byreference to the latter portions of the specification and attacheddrawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1-15 are simplified diagrams of methods according to embodimentsof the present invention; and

FIGS. 16-18 are simplified diagrams of experimental results according toembodiments of the present invention

DESCRIPTION OF THE SPECIFIC EMBODIMENTS

According to the present invention, a technique including a method anddevice for manufacturing objects is provided. In an exemplaryembodiment, the present invention provides a method for reclaimingsubstrates from a cleaving process. Such reclaimed substrates can bereused for the manufacture of other substrates and the like.

FIGS. 1-15 are simplified diagrams of methods according to embodimentsof the present invention. These diagrams are merely examples whichshould not unduly limit the scope of the claims herein. One of ordinaryskill in the art would recognize many other variations, modifications,and alternatives. Referring to FIG. 1, the present method begins byproviding a substrate 10. The substrate can be any suitable substratesuch as a silicon wafer (e.g., bulk, multilayered) and others. Thesubstrate 11 has a top surface, which is substantially planar in thisapplication. Other forms can also exist.

Optionally, a stop layer 14 is defined overlying the top surface of thesubstrate, as shown in FIG. 2. The stop layer can be any suitablematerial that protects substrate 11 and in particular surface 12 ofsubstrate 11. The stop layer can be an epitaxial silicon layer madeusing a chemical vapor deposition process. The layer can be doped orundoped. If doped, the layer can be graded or constantly doped. Thechemical vapor deposition process can include silane and hydrogenbearing gases. Other gases can also be used. These gases are introducedinto an epitaxial chamber such as those made by Applied Materials, Inc.of Santa Clara, Calif. Alternatively, the chamber can be made by ASMInternational of Phoenix, Ariz. The stop layer can also be a combinationof layers, which are doped or undoped. The stop layer can be a physicaldeposition layer or a plated layer or the like.

Next, the process includes forming a cleaving layer 18 overlying thestop layer 14, as shown in FIG. 3. The cleaving layer can be made by anysuitable material that enhances cleaving. The cleaving layer can bedeposited by one or a combination of techniques such as chemical vapordeposition, physical vapor deposition, plating, or the like. In aspecific embodiment, the cleaving layer is a silicon germanium layer.The silicon germanium layer is often made to a thickness that enhancescleaving. The silicon germanium layer can also be replaced by otherlayers, which enhance cleaving. Some of these layers have been describedin U.S. application Ser. No. 09/370,975, filed Aug. 10, 1999, now U.S.Pat. No. 6,033,974, commonly assigned, and hereby incorporated byreference.

In a preferred embodiment, the silicon germanium layer is grown in amanner where it is stable. That is, the silicon germanium is anepitaxial layer in a pseudomorphic state. The silicon germanium is notgrown in a manner to create roughening or misfit dislocations. In thepresent embodiment, a device layer is grown over the silicon germaniumto enhance stability. That is, silicon germanium, which may be in a metastable state, is now in a stable state due to the device layer orcapping layer. Details of such device layer are provided below.

Overlying the silicon germanium layer is a device layer 20, also shownin FIG. 3. The device layer is a region where active devices orstructures are to be formed in a subsequent process or processes. Thedevice layer is made of a suitable material such as silicon, forexample. The device layer can be an epitaxial silicon layer. Theepitaxial silicon layer is made overlying the silicon germanium layer ina manner where the device layer is substantially free from defects.Here, a high quality stop layer often provides an ideal source fornucleation and growth of the silicon-germanium and the overlyingepitaxial silicon layers. The epitaxial silicon layer is made using achemical vapor deposition process. The chemical vapor deposition processcan include silane and hydrogen bearing gases. These gases areintroduced into an epitaxial chamber such as those made by AppliedMaterials, Inc. of Santa Clara, Calif. Alternatively, the chamber can bemade by ASM International of Phoenix, Ariz. Depending upon theapplication, there can be an other layer(s) sandwiched between the stoplayer and the cleaving layer. Additionally, there can be an otherlayer(s) sandwiched between the cleaving layer and the device layer insome applications.

Preferably, the device layer acts as a capping layer over the cleavinglayer. The capping layer can improve stability of the cleaving layer,which is stressed due to differences in crystalline structure from thestop layer or substrate. An increase in temperature of such cleavinglayer also adds to the stress, where a temperature above a criticaltemperature for a certain film thickness creates an unstable film. In aspecific embodiment, the capping layer of epitaxial silicon improvesstability of the cleaving layer, in a manner shown in FIG. 3A. Here,thickness of silicon germanium is plotted on a vertical axis againstconcentration of germanium to silicon on a horizontal axis. Two plotsare indicated (where the silicon germanium is grown at about 550 degreesCelsius). The plot referenced as numeral 303 is shown for a silicongermanium layer, which is not capped. That is, there is no layeroverlying the silicon germanium layer. According to the plot 303, about100 Angstroms (or 80 Angstroms) of a 30% germanium mixture of silicongermanium can be grown. Region 302, which is between the two curves, isa meta stable region, where any increase in temperature from 550 degreesCelsius of the film causes an unstable condition. When the layer iscapped, however, the silicon germanium layer can be grown much thickeras shown by the curve in reference numeral 301. The capped layer allowsthe silicon germanium to be grown to a thickness of about 1.5 times ormore than two times the thickness of the uncapped layer, while stillmaintaining a stable condition during subsequent processing, such asthermal treatment (e.g., over 400 degrees Celsius) and the like.

In a specific embodiment, the present method provides a highertemperature during growth of the device layer to improve devicefabrication times. Here, the device 350 in FIGS. 3B and 3C is beingfabricated. Like reference numerals are used in this FIG. as theprevious FIGS. for cross-referencing purposes only. The devicefabricated includes substrate 11, stop layer 14, cleave layer 18, anddevice layer 340, 341. In a specific embodiment, the substrate 11 isprovided. The device also is subject to the temperature profile 310,illustrated in FIG. 3B. It is cleaned using a clean and bake process, ifdesired. The stop layer, which is epitaxial silicon, is formed overlyingthe substrate. The epitaxial silicon is formed at a first temperature,which can be about 900 to 950 degrees Celsius. Such first temperatureand epitaxial silicon fills any defects in the substrate such as crystaloriginated particles, which are called “COPs” and the like. The firsttemperature is also high enough to provide a deposition rate that isefficient for manufacturing.

Next, the cleaving layer is formed at a second temperature, which isless than the first temperature. The second temperature is a temperaturewhere a cleaving layer such as silicon germanium is stable. Such atemperature can be about 650 degrees Celsius or less for a 100 to 200Angstroms or so layer for 30% germanium in silicon, where the silicongermanium is uncapped. The layer can be grown to a thickness, where thesilicon germanium is still stable. A device layer is formed in at leasttwo steps or can be formed where it undergoes higher temperature growthduring a portion of such formation to decrease growth time. Initially,the device layer is formed at the second temperature to maintainstability in the cleave layer. In a specific embodiment, epitaxialsilicon is formed to a thickness of about 350 Angstroms or 400 Angstromsand greater to cap the cleaving layer. Once the cleave layer has beencapped, the device layer formation undergoes a higher temperature, whichdeposits such device layer at a higher deposition rate. The higherdeposition rate for epitaxial silicon can be 100 Angstroms per secondand greater. In a specific embodiment, the second device layer forms toa thickness of greater than about 1,000 Angstroms or greater than about3,000 Angstroms, but can also be at other thicknesses. The device layercan be formed in at least two steps or a number of steps to facilitatethe manufacture of the device. Additionally, the present depositionmethods are generally formed in a single chamber or a clustertoolconfiguration to eliminate any cleaning steps between layer formation.That is, the combination of the cleaving layer and the device layers canbe formed in-situ.

In a specific embodiment, the cleave layer can be deposited usingselected concentration profiles, which enhance cleaving. FIGS. 3D to 3Eare simplified diagrams of such concentration profiles for cleavinglayers according to embodiments of the present invention. As shown, thevertical axis represents concentration of germanium to silicon inpercentages and the horizontal axis represents thickness or depth from asurface region to the back side of the substrate. In FIG. 3D, the regionrepresented as reference numeral 371 is the cleaving layer. Here, theconcentration of germanium is zero at position t(1), which is also puresilicon. The germanium concentration steps up to a selectedconcentration (e.g., 30%), the concentration then decreases linearlyback down to zero at t(2). Cleaving generally occurs at around positiont(1), which has a higher stress than the other regions and would be thelocation of the cleave plane.

In FIG. 3E, the region represented as reference numeral 381 is thecleaving layer. Here, the concentration of germanium is zero at positiont(1), which is also pure silicon. The germanium concentration steps upto a selected concentration (e.g., 30%) and maintains the selectedconcentration through the region referenced as numeral 382. Thegermanium concentration then decreases linearly back down to zero att(2). Cleaving occurs at around position t(1) (the cleave planelocation), which has a higher stress than the other regions at someselected implant conditions. Depending upon the application, region 382can also include a slope, which is linear or curved, depending upon theapplication.

Generally, the profiles illustrated by the above FIGS. include at leasttwo regions, but may include more depending upon the application. Here,the first region, which is in the vicinity of t(1), is the cleave region(i.e. the cleave plane), which should have a higher stress than thesecond region, which is between the cleave region and position t(2). Thesecond region is the capture region. The capture region is a portion ofthe cleave region, which enhances an efficient capture andredistribution of particles implanted within this layer duringimplantation or subsequent process steps. Once the particles have beencaptured, they can redistribute to add stress to the cleave region.Details of such introduction of particles are described below.

Preferably, the method introduces particles 22 through the device layerinto the cleaving layer 18, as shown in FIG. 4. Depending upon theapplication, smaller mass particles are generally selected to reduce apossibility of damage to the device layer 22. That is, smaller massparticles easily travel through the device layer to the cleaving layerwithout substantially damaging the device layer that the particlestraverse through. For example, the smaller mass particles (or energeticparticles) can be almost any charged (e.g., positive or negative) and/orneutral atoms or molecules, or electrons, or the like. In a specificembodiment, the particles can be neutral and/or charged particlesincluding ions such as ions of hydrogen and its isotopes (i.e.,deuterium), rare gas ions such as helium and its isotopes, and neon. Theparticles can also be derived from compounds such as gases, e.g.,hydrogen gas, water vapor, methane, and hydrogen compounds, and otherlight atomic mass particles. Alternatively, the particles can be anycombination of the above particles, and/or ions and/or molecular speciesand/or atomic species. The particles generally have sufficient kineticenergy to penetrate through the surface to a selected depth underneaththe surface of the device layer.

Using hydrogen as the implanted species into the silicon wafer as anexample, the implantation process is performed using a specific set ofconditions. Implantation dose ranges from about 10¹⁴ to about 10¹⁷atoms/cm², and preferably the dose is greater than about 10¹⁵ atoms/cm².Implantation energy ranges from about 1 KeV to about 1 MeV , and isgenerally about 30 KeV. Implantation temperature ranges from about −200to about 600° C., and is preferably less than about 400° C. to prevent apossibility of a substantial quantity of hydrogen ions from diffusingout of the implanted silicon wafer and annealing the implanted damageand stress. The hydrogen ions can be selectively introduced into thesilicon wafer to the selected depth at an accuracy of about +/−0.03 to+/−0.05 microns. Of course, the type of ion used and process conditionsdepend upon the application.

In an alternative embodiment, chemical, amorphization, interstitial, andor other stress can be introduced by adding heavier particles to thecleaving layer. Here, the heavier particles include one or anycombination of silicon, oxygen, germanium, carbon, nitrogen, or anyother suitable heavier particle that can add stress and enhancecleaving. These heavier particles can be implanted through the devicelayer or can be diffused or the like. In a specific embodiment, a doserequirement for these heavier particles would generally be less thanthat of lighter particles but do often require higher implant energiesthan lighter ions to penetrate to the vicinity of the cleave layer. Fordevice layer ranges of 1500-2500 Angstroms or so, implant energies couldrange from 80-200 keV for ions between the mass range of oxygen andsilicon. A combination of heavier and lighter particles can also be usedin other embodiments. In these embodiments, virtual no microbubbles orcavities are formed. Additionally, redistribution of such heavierparticles may not take place or occurs less than lighter particles.Depending upon the application, many other ways of introducing stresscan also be used.

Effectively, the implanted particles add stress or reduce fractureenergy along a region parallel to the top surface of the substrate atthe selected depth. The energies depend, in part, upon the implantationspecies and conditions. These particles reduce a fracture energy levelof the substrate at the selected depth. This allows for a controlledcleave along the implanted plane at the selected depth. Implantation canoccur under conditions such that the energy state of substrate at allinternal locations is insufficient to initiate a non-reversible fracture(i.e., separation or cleaving) in the substrate material. It should benoted, however, that implantation does generally cause a certain amountof defects (e.g., micro-defects) in the substrate that can be repairedby subsequent heat treatment, e.g., thermal annealing or rapid thermalannealing.

In some embodiments, the particles are introduced into the cleavinglayer to achieve a selected dosage to facilitate cleaving. Referring toFIGS. 4A to 4B, the present invention provides selected dosages that canbe implanted into the cleaving layer to enhance cleaving. In each of theFIGS. the vertical axis represents concentration of particles, and ahorizontal axis represents thickness or depth from a surface of thesubstrate to the back side of the substrate. The cleaving layer is shownby the cross-hatched lines 401, which are between positions t(1) andt(2). FIG. 4A illustrates the conventional process taught by Bruelgenerally for comparison purposes only. Here, Bruel's techniqueintroduces a high concentration of hydrogen bearing particles where themaximum dosage intersects the cleaving region, which is a purelyimplanted layer 401A. Here, a certain amount of dosage (C_(c)) isgenerally used in the cleaving layer to facilitate the Bruel method. TheBruel method uses a high concentration of hydrogen to form microbubbles,which form even larger bubbles, which blister, splinter, and separatethe film during thermal treatment. This high concentration generally isundesirable since it causes excessive surface roughness and otherdefects, which the present invention overcomes. Additionally, thermaltreatment at high temperature is also generally undesirable, since itcauses defects.

Referring to FIG. 4B, the present method uses a selected low dosage ofhydrogen bearing particles, which occupy a region between position t(1)and t(2). The cleaving layer referenced as numeral 401 comprises adeposited silicon germanium layer and implanted particles, which are ina low dose. The dose is defined as an amount that is substantially freefrom the formation of microbubbles, which can lead to even largerbubbles, which blister, splinter, and separate the film. The dosegenerally should be a certain amount of particles that occupy the regionin the cleaving layer. Regions outside the cleaving layer can have ahigher dose, but generally do not directly participate in the cleavingprocess.

As shown, the particle distribution profile can include, for example,those shown by reference numbers 409, 407, and 405. Profile 405generally has a higher overall dose than either profile 407 or 409,which has the lowest overall dose. The higher dose occupies region 415,which is outside of the device layer 411, thereby reducing a possibilityof high dosage damage to the device layer. The cleaving layer has arelatively constant amount of dosage in these examples. The constantamount of dosage is maintained where damage to the device layer isreduced. In these embodiments, a maximum dosage region falls outside ofthe cleave layer, which is substantially different from the conventionalBruel process where a maximum dosage region is necessarily in closeproximity and directly contributes to the conventional blisteringcleaving processes. Therefore, it is a fundamental characteristic of theBruel blistering processes that the cleave plane will be at or very nearto the implant peak in a region where the microcavities and microbubblescoalesce to develop a fracture plane.

Preferably, the cleaving layer has a suitable characteristic forcleaving after implantation. The cleaving layer is a stressed layer. Thestressed layer is thermally stable after implantation, since it ispreferable that dislocations are not formed in the stressed layer afterits formation. That is, dislocations are generally not desirable. Thesedislocations can come in the form of slip planes, stacking faults,dislocations, and the like, which can often combine and form largerstructures during a thermal treatment process. The present cleavingplane is also free from microbubbles or microcavities, which can formmacrobubbles, and separation. Accordingly, the implantation often mustbe carried out in a manner and a dose to prevent such dislocations inpreferred embodiments.

Once particles have been introduced into the cleaving layer, the donorsubstrate can be bonded to a handle substrate. Here, optionally, a stepof low temperature plasma activation can be used to clean faces of thesubstrates. Then, the substrates are bonded together. A thermaltreatment step can follow the bonding step to improve bond integrity. Ina specific embodiment, the thermal treatment step temperature/timecombination can also cause the particles to redistribute to each of theinterfaces between the cleaving layer and the device layer (and the stoplayer or substrate). The thermal treatment step redistributes suchparticles after implantation to form at least one maximum peak (or morecan be formed) near the interfaces of the cleaving layer. In anembodiment using a silicon germanium cleaving layer and an epitaxialsilicon device layer, the present invention provides a higher maximum inthe interface between the silicon germanium and the epitaxial layer orthe other interface. In certain embodiments, the particles can alsoredistribute during implantation or other thermal processtime/temperature combinations.

A controlled cleaving process is performed, as shown in FIG. 5. Here,the donor substrate 11 has been bonded to a handle substrate 22. Bondingcan occur using a variety of techniques to attach substrate 11 tosubstrate 22. In a specific embodiment, a silicon dioxide layer 24 canbe used to attach these substrates together to form a multilayeredsubstrate structure. In a specific embodiment, the bonded substratesundergo a step of selective energy placement or positioning or targetingwhich provides a controlled cleaving action at the stressed region alongthe cleave plane. In preferred embodiments, selected energy placementoccurs near an edge or comer region of the stressed region of substrate.The impulse or impulses arc provided using energy sources. Examples ofsources include, among others, a chemical source, a mechanical source,an electrical source, and a thermal sink or source. The chemical sourcecan include a variety such as particles, fluids, gases, or liquids.These sources can also include chemical reaction to increase stress inthe stressed region. The chemical source is introduced as flood,time-varying, spatially varying, or continuous. In other embodiments, amechanical source is derived from rotational, translational,compressional, expansional, or ultrasonic energies. The mechanicalsource can be introduced as flood, time-varying, spatially varying, orcontinuous. In further embodiments, the electrical source is selectedfrom an applied voltage or an applied electromagnetic field, which isintroduced as flood, time-varying, spatially varying, or continuous. Instill further embodiments, the thermal source or sink is selected fromradiation, convection, or conduction. This thermal source can beselected from, among others, a photon beam, a fluid source, a liquidsource, a gas source, an electro/magnetic field, an electron beam, athermo-electric heating, a furnace, and the like. The thermal sink canbe selected from a fluid source, a liquid source, a gas source, acryogenic fluid, a super-cooled liquid, a thermoelectric cooling means,an electro/magnetic field, and others. Similar to the previousembodiments, the thermal source is applied as flood, time-varying,spatially varying, or continuous. Still further, any of the aboveembodiments can be combined or even separated, depending upon theapplication. Of course, the type of source used depends upon theapplication. In a specific embodiment, the energy source can be a fluidsource that is pressurized (e.g., compressional) according to anembodiment of the present invention. A detailed discussion of such apressurized fluid source is described in U.S. application Ser. No.09/370,975, filed Aug. 10, 1999 now U.S. Pat. No. 6,033,974 which isincorporated by reference herein.

As shown, cleaving separates the donor substrate from the handlesubstrate, where the device layer is attached to the donor handlesubstrate, as shown in FIG. 6. As shown, each of the substrates includesa portion 18 of the cleaving layer. The cleaving layer is selectivelyremoved from the handle wafer substrate. Here, such selective removalprocess can include dry or plasma etching, wet etch, polishing, or anycombination of these. In one embodiment, the removal process uses aconcentrated solution of hydrogen fluoride, which is mixed with nitricacid and acetic acid. Alternatively, the removal process uses aconcentrated solution of hydrofluoric acid, which is mixed with hydrogenperoxide and acetic acid. The selectivity of such solution is preferablygreater than about 100:1 or greater than about 200:1 (etch rate ofcleaving layer to etch rate of stop layer).

The cleaving layer is selectively removed from the donor substrate, asshown in FIG. 7. A similar selective removal process can be used toremove the cleaving layer from the donor substrate. Here, such selectiveremoval process can include dry or plasma etching, wet etch, polishing,or any combination of these. In one embodiment, the removal process usesa concentrated solution of hydrogen fluoride, which is mixed with nitricacid and acetic acid. Alternatively, the removal process uses aconcentrated solution of hydrofluoric acid, which is mixed with hydrogenperoxide and acetic acid. The selectivity of such solution is preferablygreater than about 100:1 or greater than about 200:1 (etch rate ofcleaving layer to etch rate of stop layer).

Once the cleaving layer has been removed, the stop layer is exposed, asshown in FIG. 8. Here, the top surface 16 of the stop layer is exposedand substantially free from defects. The donor substrate with stop layercan be reused in another substrate fabrication process. In otherembodiments, the stop layer is removed in a selective manner. In theseembodiments, there may be some implant damage in the stop layer, whichshould be taken out before formation of a cleaving layer thereon. Thestop layer is selectively removed from the donor substrate to expose thetop surface of it. Now, the donor substrate is ready for another seriesof processing steps to form a multilayered substrate structure. In aspecific embodiment, the stop layer can be removed. A smoothing step mayfollow the removing process. Alternatively, the stop layer can besmoothed using a combination of hydrogen treatment and heat treatment.An example of such smoothing process is described in U.S. applicationSer. No. 09/295,858, filed Apr. 21, 1999, now U.S. Pat. No. 6,171,965,commonly assigned, and hereby incorporated by reference for allpurposes.

In an alternative embodiment, the present process can be repeated toform a multilayered donor substrate structure 100 of FIG. 10. Here, thedonor substrate structure 100 includes a stop layer 103 overlying thedonor substrate. A cleaving layer 105 is formed overlying the stop layer103. Another stop layer 107 is formed overlying the cleaving layer 105and another cleaving layer 109 is formed overlying the stop layer 107. Adevice layer 111 is formed overlying the cleaving layer. In a specificembodiment, the implant of particles can be selectively adjusted alongthe z-direction of the substrate structure, where a higher dose isprovided to either cleaving layer 109 or cleaving layer 105. Dependingupon where the higher dose is provided, cleaving can occur at cleavinglayer 109 or cleaving layer 105. If the implant profile provided a highconcentration region 113, cleaving would occur at cleaving plane 115 ina specific embodiment. Cleaving can occur using a variety of techniquesuch as the CCP described in U.S. application Ser. No. 09/370,975, filedAug. 10, 1999, now U.S. Pat. No. 6,033,974 which is commonly owned andincorporated by reference herein.

In an alternative embodiment, the present process can be repeated toform a multilayered donor substrate structure 200 of FIG. 11. Here, thedonor substrate structure 200 includes bulk substrate 202. Overlyingbulk substrate is a stop layer 201. A cleaving layer 203 is formedoverlying the stop layer 201. Another stop layer 205 is formed overlyingthe cleaving layer and another cleaving layer 207 is formed overlyingthe stop layer 205. An nth stop layer 209 is formed overlying thecleaving layer. An nth cleaving layer is formed overlying the nth stoplayer. A device layer 213 is formed overlying the cleaving layer. In aspecific embodiment, the implant of particles can be selectivelyadjusted along the z-direction of the substrate structure, where ahigher dose is provided to either of the cleaving layers. Depending uponwhere the higher dose is provided, cleaving can occur at a particularcleaving layer. If the implant profile provided a high concentrationregion 215, cleaving would occur at cleaving plane 217 in a specificembodiment. Cleaving can occur using a variety of technique such as theCCP described in U.S. application Ser. No. 09/370,975, filed Aug. 10,1999, now U.S. Pat. No. 6,033,974 which is commonly owned andincorporated by reference herein.

Optionally, the present method uses a selective pattern distributiontechnique of particles in the cleaving layer to enhance cleaving, asillustrated in diagrams of FIGS. 12 to 15. These diagrams are merelyexamples, which should not limit the scope of the claims herein. One ofordinary skill in the art would recognize many other variations,modifications, and alternatives. Some of the reference numerals usedherein are similar to the previous ones for cross referencing purposesonly. As shown, the present method begins by providing substrate 11,which can be a substrate such as the one in FIG. 4, as well as others.That is, it is not necessary that the cleave layer include a depositedlayer. The cleave layer can be solely an implanted layer, whereparticles 130 have been introduced into the substrate.

Once the cleave layer has been formed, the method yields a substratesuch as the one in FIG. 13. As shown are substrate 11, cleave layer 160,and device layer 120, which can be silicon, epitaxial silicon, oranother material. Particles 150 are selectively introduced into an edgeregion 180 of the cleave layer in another implantation step or a secondstage (or another stage) of the implantation step of introducingparticles 22. The edge region can be only on one end of the substrate.Alternatively, the edge region can be around a periphery of thesubstrate. The edge region is generally a higher concentration region,which is used to facilitate cleaving or initiation of cleaving. The edgeregion extends from an outer edge of the substrate to a length delta, asshown. A profile 151 of the edge region is illustrated by a simplifieddiagram in FIG. 14. Here, the diagram includes a vertical axis, whichplots concentration, and a horizontal axis, which plots length from theedge 153 of the substrate to a center region 154 of the substrate. Thedistribution of particles can include a step distribution, a gradeddistribution, or any other distribution, which facilitates cleaving orinitiation of cleaving.

Once the substrate has been selectively implanted, substrate 11 isbonded to substrate 20. The substrates can be bonded to each otherthrough interface 220, which can be silicon dioxide or the like. Manyother types of interfaces can also be used. Here, a controlled cleavingprocess can be used. Other types of cleaving techniques can also be useddepending upon the application.

The present invention also provides many advantages and/or benefits overconventional processes. For example, the present invention can besubstantially free from the use of porous silicon or masked area in someembodiments. Accordingly, the present device layer would therefore be ofa higher quality than conventional layers. Additionally, the presentinvention provides for a higher quality epitaxial layer, which is formedon a high quality cleave layer that is generally free from dislocationsand the like. In other embodiments, the present cleave layer comprises anon-contaminating, process compatible and miscible with a single crystalalloy. Here, the present process can be performed through the use of aclustertool system, which allows for an in-situ process for forming astop layer, a cleaving layer, a device layer, or any combination ofthese. Additionally, the present cleave layer can be stable (e.g.,thermally) under subsequent processing and allow high-temperature steps(e.g., greater than 400 degrees Celsius, or greater than 500 degreesCelsius) such as oxidation to be performed. Furthermore, the use of lowdoses of an implanted specie provides for higher productivity (e.g., twotimes, three times, or five times and greater) and lower device layerdamage Dose/implant depth process tradeoff would also generally allowthe cleave plane and device layer to be physically separated from theimplant peak and end-of-range (EOR) damage, which prevents damage to thedevice layer from any thermal treatment, if any. The present inventionalso provides a process where the cleave layer, after separation at thecleave plane, allows selective etching to remove the cleave layermaterial using conventional etching chemicals. Depending upon theembodiment, one or more of these benefits may exist.

Although the above has been generally described in terms of a specificsubstrate, many others can also exist. These substrates can include,among others, gallium arsenide, quartz, and silicon carbide. Of course,the type of substrate used depends upon the application.

EXAMPLE

To prove the principle and operation of the present invention, anexperiment was performed. In this experiment, we used eight-inch bulk CZwafers. These wafers were prime low boron concentration wafers fromMitsubishi Silicon America. The wafers were cleaned using a conventionalSC1 and SC2 clean. Next, the wafers were dried using a conventional spinrinse dry so that the wafers were free from liquid droplets. Each waferwas loaded into an epitaxial silicon reactor. The reactor was a toolmade by ASM International of Phoenix, Arizona, but is not limited tosuch reactor. A high temperature bake at about 1,100 Celsius wasperformed on the wafer. This bake removed native oxide and cleaned facesof the wafer. The bake was followed by a deposition process, where about2,000 Angstroms of epitaxial silicon was deposited.

Such deposition was provided by a combination of silane and hydrogengases in a conventional manner.

Next, the method used a deposition of silicon germanium overlying theepitaxial silicon. The silicon germanium was introduced into the samechamber as the epitaxial silicon, where the wafer remained. The gasesused included germane (GeH₄) and silane gases. The silicon germanium wasabout 30% germanium and about 70% silicon. Other concentrations ofgermanium can also be used. Hydrogen gas continued to be introducedduring the introduction of the germane and silane gases. Suchintroduction occurred in-situ, where the wafer was not allowed outsideof the chamber to prevent a possibility of contamination on the surfaceof the epitaxial silicon layer. Here, a continuous growth process of thestop layer and the cleaving layer was provided. The silicon germaniumwas grown at a temperature that prevented misfits and other structuraldefects. Such temperature is about 700 degrees Celsius and less. In thisexperiment, the cleave layer thickness was about 200 Angstroms.

Next, the method used a deposition of epitaxial silicon overlying thesilicon germanium layer. Here, germane gas was turned off in thechamber, while the silane and hydrogen gases were allowed to continue toenter the chamber. A higher flow rate of such gases could be introducedto improve deposition rates. The epitaxial silicon layer was growth to athickness of 2200 Angstroms.

Once the deposition processes were completed, the wafer was implanted.Optionally, the surface of the epitaxial silicon can be oxidized, wherea thermal oxide layer of about 1000 Angstroms is grown. The implantationprocess was provided in a hydrogen implanter. The implanter was aconventional Varian implantation apparatus, but is not limited to suchapparatus. The hydrogen was introduced at a dose of about 3×10¹⁶atoms/cm² at an energy of about 22 keV. It is believed that the hydrogenincreases stress in the silicon germanium layer. In some recentexperiments, doses of less than 8×10¹⁵ atoms/cm² at an energy of about22 keV were also shown to cleave. Lower doses can be realized throughthe use of thicker cleave layers.

The implanted surface of the substrate was then bonded to a handlewafer. Here, the faces of each of the substrates were plasma activatedusing an oxygen plasma. Next, the faces were brought together and bondedto each other to form a suitable bond that does not separate during thepresent cleaving method. Bonding was perfected using a thermal treatmentprocess of 350 degrees Celsius for 2 hours which enhanced the bond. Thethermal treatment process occurred and was maintained at a temperaturebelow gaseous microbubble or microcavity formation along the cleaveplane. Additionally such treatment process occurred at such temperaturebelow crystalline rearrangement (e.g., blistering), surface morphologychange, or separation of the implanted material. It has been found thatsuch blistering and high temperature caused film quality problems andthe like, which have been undesirable. In fact, it is generallyunderstood that the blister process no longer functions for doses below3.5×10¹⁶ atoms/cm² at any implant energies and about 4.4×10¹⁶ atoms/cm²at about 22 keV under any thermal treatment temperatures and times.

An example of an implant profile is shown in FIG. 16, which is asimplified diagram 1300 of an experimental result according to anembodiment of the present invention. This diagram is merely an example.There could be many other variations, modifications, and alternatives.The diagram plots concentration (atoms/cubic centimeters) along thevertical axis and a horizontal axis, which is depth. Such depth extendsfrom the top surface of the device layer, through the cleave layer, andto the substrate. As shown, the diagram illustrates a plot of hydrogenions 1301, which has a maximum concentration 1307. The cleaving layer1305, which is silicon germanium, is also shown. Upon cleaving, thecleaving layer separates the device layer from the substrate in a regiondefined as the cleave plane shown by reference numeral 1309. Such regionaccumulates hydrogen, which increases interfacial stress, whichfacilitates cleaving. Cleaving occurred in a cleaving apparatus, such asthe one described in U.S. application Ser. No. 09/371,906, filed Aug.10, 1999 which is incorporated by reference herein. Once cleavingseparated the two substrates from each other, the cleaving process wasterminated. Any remaining cleaving layer (i.e., silicon germanium) wasselectively removed from the stop layer, which was epitaxial silicon.

FIGS. 17 and 18 are micrographs of surface roughness of cleaved films.Referring to FIG. 17, surface roughness of a conventional blisterseparation process known as Smart Cut™ was performed. Such conventionalprocess uses high doses of hydrogen (>6×10¹⁶ atoms/cm² at about 22 keV),which is implanted into a substrate. The substrate is bonded and thensubjected to high temperature. The high temperature providesmicrobubbles, which turn into macrobubbles, which ultimately blister adevice layer from the substrate. Since such high concentrations and hightemperatures are used, the surface roughness often is about 80 AngstromsRMS and greater. In contrast, the present process using a controlledcleaving process, which uses a silicon germanium cleaving layer. Thepresent process provides a much smoother surface than the conventionalprocess. Here, we measured a surface roughness value of 10 to 12Angstroms RMS. After stripping the cleaving layer, the surface roughnesswas about 4 to 6 Angstroms RMS. Accordingly, the present processprovides much smoother films than conventional processes due to asubstantially different physical mechanism in cleaving. The presentexperiment demonstrates many of the aspects of the present inventiondescribed herein. This experiment, however, is not intended to undulylimit the scope of the claims herein. One of ordinary skill in the artwould recognize many variations, alternatives, and modifications.

While the above is a full description of the specific embodiments,various modifications, alternative constructions and equivalents may beused. Therefore, the above description and illustrations should not betaken as limiting the scope of the present invention which is defined bythe appended claims.

1. A method of forming substrates, the method comprising: providing adonor substrate; forming a cleave layer comprising a cleave plane on thedonor substrate, the cleave layer comprising silicon germanium; forminga device layer on the cleave layer, the device layer comprisingepitaxial silicon; introducing particles into the cleave layer to addstress to the cleave plane, where the particles are introduced in amanner substantially free from microbubble or microcavity formation ofthe particles along the cleave plane within the cleave layer;redistributing a portion of the particles within the cleave layer toform a higher concentration region of the particles in a region in avicinity of the cleave plane, where the distribution is carried out in amanner substantially free from microbubble or microcavity formation ofthe particles along the cleave plane within the cleave layer; providingselected energy to the donor substrate to cleave the device layer at thecleave plane, whereupon the selected energy is applied to create acontrolled cleaving action to remove the device layer from a portion ofthe cleave layer in a controlled manner.
 2. The method of claim 1further comprising bonding the device layer of the donor substrate to ahandle wafer after introducing the particles.
 3. The method of claim 1wherein the silicon germanium in the cleave layer comprises at least 10%germanium content in the silicon germanium alloy.
 4. The method of claim1 wherein the substrate comprises a stop layer underlying the cleavelayer.
 5. The method of claim 1 wherein a cleaved surface of the devicelayer comprises a surface roughness of less than about 20 Angstroms RMS.6. The method of claim 1 wherein the particles are selected fromhydrogen ions, deuterium ions, helium ions, or other light atomic massspecies.
 7. The method of claim 4 wherein the stop layer comprises afirst stop layer overlying the substrate, a first silicon germaniumlayer overlying the first stop layer, and a second stop layer overlyingthe first silicon germanium layer.
 8. The method of claim 1 wherein thecleave layer comprises a particle collection region and a cleave region.9. The method of claim 1 wherein the cleave layer comprises a gradedconcentration of the silicon germanium.
 10. The method of claim 9wherein the graded concentration is greater near the device layer anddecreases toward the donor substrate.
 11. A method of forming amultilayered substrate, the method comprising: providing a donorsubstrate; forming a cleave layer comprising a cleave plane on the donorsubstrate, the cleave layer comprising silicon germanium; forming adevice layer on the cleave layer, the device layer comprising epitaxialsilicon; introducing particles into the cleave layer to add stress inthe cleave layer, where the particles are introduced in a mannersubstantially free from microbubble or microcavity formation of theparticles along the cleave plane within the cleave layer; bonding ahandle substrate on the cleave layer; redistributing a portion of theparticles within the cleave layer to form a higher concentration of theparticles in a region in the vicinity of the cleave plane, where theredistribution is carried out in a manner substantially free frommicrobubble or microcavity formation of the particles along the cleaveplane within the cleave plane; providing selected energy to the donorsubstrate to cleave the device layer at the cleave plane, whereupon theselected energy is applied to create a controlled cleaving action toremove the device layer from a portion of the cleave layer in acontrolled manner to separate the handle substrate that has the devicelayer from the donor substrate.
 12. The method of claim 11 wherein thecleave layer is a silicon germanium layer and the device layer is anepitaxial silicon layer.
 13. A method of forming substrates, the methodcomprising; providing a donor substrate; forming a cleave layercomprising a cleave plane on the donor substrate, the cleave layercomprising silicon germanium; forming a device layer on the cleavelayer, the device layer comprising epitaxial silicon; introducingparticles into the cleave layer to add stress to the cleave plane, wherethe particles are selected from those species that are derived free fromhydrogen gas, helium gas, or any other species that forms microbubblesor microcavities; and separating the device layer from the donorsubstrate at the cleave plane of the donor substrate by a controlledcleaving action.
 14. The method of claim 13 further comprising bondingthe device layer of the donor substrate to a handle substrate.
 15. Themethod of claim 14 wherein the separating removes the device layer fromthe donor substrate, the handle substrate comprising the device layer.16. The method of claim 1 wherein the cleave plane is disposed in thecleave layer at about a depth of highest concentration of germanium inthe cleave layer.